Bug 2525703 (CVE-2026-55520)

Summary:	CVE-2026-55520 protego: Protego: Denial of Service via exponential backtracking in robots.txt URL wildcard matching
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security DevOps Team <prodsec-dev>
Status:	NEW ---	QA Contact:
Severity:	medium	Docs Contact:
Priority:	medium
Version:	unspecified	Keywords:	Security
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Hardware:	All
OS:	Linux
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Doc Text:	A flaw was found in Protego, a pure-Python robots.txt parser. A remote attacker could exploit this vulnerability by providing a crafted robots.txt file containing numerous asterisks in Allow or Disallow directives. This causes exponential backtracking during URL wildcard matching, leading to a Regular Expression Denial of Service (ReDoS) condition. This can result in the `protego.Protego.can_fetch` function spending an attacker-controlled period matching a URL, thereby denying service to the crawler.	Story Points:	---
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oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
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Bug Depends On:	2526711
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Description OSIDB Bzimport 2026-08-28 19:44:33 UTC

Protego is a pure-Python robots.txt parser with support for modern conventions. Prior to 0.6.2, protego._urlpattern._URLPattern._prepare_pattern_for_regex translates every asterisk in an Allow or Disallow directive into a lazy regular-expression wildcard, so a directive containing many asterisks creates exponential backtracking. After protego.Protego.parse processes a crafted robots.txt file, protego.Protego.can_fetch can spend an attacker-controlled period matching a near-miss URL and deny service to the crawler. The vulnerable path is src/protego/_urlpattern.py in the _URLPattern match logic. This issue is fixed in version 0.6.2.